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Message-ID: <0afe3f35-1b25-d1c6-89bb-8dae7a4070e9@cantab.net>
Date: Thu, 17 Nov 2022 12:54:51 +0000
From: David Vrabel <dvrabel@...tab.net>
To: Marek Marczykowski-Górecki
<marmarek@...isiblethingslab.com>, linux-kernel@...r.kernel.org
Cc: Juergen Gross <jgross@...e.com>,
Stefano Stabellini <sstabellini@...nel.org>,
Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
Jan Beulich <jbeulich@...e.com>,
"moderated list:XEN HYPERVISOR INTERFACE"
<xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH] xen-pciback: Consider MSI-X enabled only when MASKALL bit
is cleared
On 17/11/2022 11:41, Marek Marczykowski-Górecki wrote:
> Linux enables MSI-X before disabling INTx, but keeps MSI-X masked until
> the table is filled. Then it disables INTx just before clearing MASKALL
> bit. Currently this approach is rejected by xen-pciback.
> Allow setting PCI_MSIX_FLAGS_ENABLE while INTx is still enabled as long
> as PCI_MSIX_FLAGS_MASKALL is set too.
The use of MSI-X interrupts is conditional on only the MSI-X Enable bit.
Setting MSI-X Enable effectively overrides the Interrupt Disable bit in
the Command register.
PCIe 6.0.1 section 7.7.2.2. "MSI-X Enable ... is prohibited from using
INTx interrupts (if implemented)." And there is similar wording for MSI
Enable.
I think you need to shuffle the checks for MSI/MSI-X in
xen_pcibk_get_interrupt_type() so they are _before_ the check of the
Interrupt Disable bit in the Command register.
David
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